The pulmonary capillary endothelium is sensitive to injury by high oxygen atmospheres. The destruction of the pulmonary endothelium leads to many of the symptoms of oxygen toxicity and is the primary factor leading to death from oxygen exposures. One of the best postulates to explain the mechanism of oxygen injury to the endothelium is the formation of free radicals of oxygen. The extreme reactivity of radicalized oxygen molecules could lead to molecular damage characteristic of oxygen poisoning. A number of studies have shown that superoxide dismutase may protect against oxygen toxicity by dismuting the superoxide free radical. However, no studies have attempted to demonstrate the rate of production and the sites of production of the superoxide radical in a mammalian model. Our research objectives are: (1) to determine whether or not high tissue oxygen tensions are associated with an increased production of superoxide free radicals in pulmonary capillary endothelial cells and (2) to determine the major metabolic pathways that are responsible for producing superoxide free radicals. Well developed methods for measuring superoxide flux are available but in order to apply them to crude tissue extracts it is essential that the superoxide dismutases be removed. This will be done using specific antisera and an immunoprecipitation technique. Both whole rat lungs and cultured rat lung endothelial cells will be studied. In order to determine whether or not the cultured endothelial cells are an appropriate model for in vivo endothelial cells, extensive morphological and morphometric studies of the cultured cells will be done.